Topic: CB550f 77 starting problems

[realmellow]

Hi, I have a 1977 CB550f which when i bought it had been sat for a few years and quite neglected. I took it on as a project to restore despite never really having done anything like this before, although I have always had bikes and mostly did any repairs myself.

I replaced the battery, new plugs, fresh fuel and new ignition coils. My problem is that the bike still won't fire up, it has two strong blue sparks off one of the coils but nothing from the other (left) which are the blue are yellow wires. I used a multimeter to check the volts on the coil not firing (blue and yellow) but nothing read back. These wires lead back to the ignition timing which is where I'm lost. Could it be the earth on the ignition timing? If so, where is that located?

Apologies if my diagnosis seems really basic, this is a huge learning curve for me.
Many thanks for any input.

[Deltarider]

Remove chrome cover of the ignition (right hand side) and have a close look at the ignition.
The contactbreakers provide ground to the coils. When the contactbreaker opens, the coil sends it's energy through the HT leads to the sparkplugs that will spark. So when the ignition key is switched ON and the kill switch on the right handlebar is in RUN you can do a simple test. As soon as the contactbreaker opens you should read voltage between the wire connected to that particular contactbreaker and ground. It should be between 10 - 12 Volts. When all is fine, you can even hear the plugs spark the moment you open the points. If you don't read volts, then the first thing to inspect is if maybe the connectors on that contactbreaker are accidentely making contact with the plate it is mounted on. In that case your contactbreaker, even when open, still grounds and you will not read any volts and the whole idea of stimulating the coil is lost (the same goes if that contactbreaker happens to be so maladjusted that it doesn't open at all during rotation). If the connectors do not touch the plate, you could disconnect the blue (or yellow) wire and then see if you measure volts between that wire and ground. If you still read no volts you should check for continuity from where the blue or the yellow wire leaves the coil and the end of that wire at the points. It could be that halfway a connector has come loose. Ofcourse you must also check if both coils receive 12V+ by the black/white wire. If not, also there a connector can be loose. There are some more tests but please report back first.

[Bankerdanny]

Read through this thread, it will help you work through what should be connected where and what to measure:

http://forums.sohc4.net/index.php/topic,158041.0.html

[Deltarider]

Bankerdanny, I'm guiding him step by step. It's not much use overloading him with all that. It's too much.

[calj737]

I used a multimeter to check the volts on the coil not firing (blue and yellow) but nothing read back.

Can you explain exactly how you tested this?

[realmellow]

Thank you Deltarider, I have tomorrow off work so I will get straight to your suggestions then.

I used a multimeter to check the volts on the coil not firing (blue and yellow) but nothing read back.

Can you explain exactly how you tested this?

I turned the key, set meter to 20v, I then earthed against the engine block and placed the positive wire onto both connectors to the (right side) coil. Just like I did with the other coil when I got the right readings. Is that the correct way?

[calj737]

You would only read voltage across the BLK/Wht wire, never across Blue or Yellow.